1. Field of the Invention
The present invention relates to a multi-layer fuel tube which allows little permeation of an alcohol/gasoline mixed fuel or the like through the tube wall, is excellent in properties including impact resistance, and is particularly suitable for a multi-layer fuel tube used in an automobile.
2. The Description of the Related Art
Fuel tubes conventionally used for automobiles are made of a metal or a resin. However, substitution of resin tubes for metal tubes is recently being investigated in order to solve the problem of corrosion by anti-freezing agents and in order to respond to the requests for reducing the weight of automobile bodies for the purpose of improving fuel efficiency.
Resin tubes, however, allow considerable permeation of fuel through the tube walls in comparison with the metal tubes. Particularly, conventional tubes of polyamide 11 resin or polyamide 12 resin allow permeation by alcohols. To use such a resin fuel tube for an alcohol/gasoline mixed fuel, the thickness of the tube must be increased, which disadvantageously results in reducing the flexibility of the tube and increasing the weight and the cost of the material and, thus, decreased productivity. Also, resin tubes do not have suitable properties, including the impact resistance at low temperatures and stiffness, to be used under severe conditions as automobile fuel tubes.
To solve the above problems, Japanese Unexamined Patent Publication (Kokai) No. 5-293916 proposes a multi-layer tube, for fuels, which comprises a polyamide resin containing 1.5 to 10% by weight of a layered silicate uniformly dispersed therein. However, this fuel tube of a resin composition still does not sufficiently prevent permeation of an alcohol/gasoline mixed fuel through the tube walls.
The object of the present invention is to solve the problems of the prior art, that is, to provide a multi-layer fuel tube which can significantly reduce or prevent the permeation of an alcohol/gasoline mixed fuel through the tube walls and has excellent properties such as the impact resistance at low temperatures and stiffness.
The present invention resides in a multi-layer fuel tube comprising at least three thermoplastic resin layers, said at least three thermoplastic resin layers comprising (A) a layer of polyamide 11 resin and/or polyamide 12 resin, (B) a layer of polyamide 6, and (C) a layer of polyamide containing 0.05 to 30% by weight of a layered silicate uniformly dispersed therein.